SG: Change sg_set_page() to take length and offset argument

Most drivers need to set length and offset as well, so may as well fold
those three lines into one.

Add sg_assign_page() for those two locations that only needed to set
the page, where the offset/length is set outside of the function context.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/include/asm-frv/scatterlist.h b/include/asm-frv/scatterlist.h
index 99ba76e..2e7143b 100644
--- a/include/asm-frv/scatterlist.h
+++ b/include/asm-frv/scatterlist.h
@@ -16,8 +16,7 @@
  *
  * can be rewritten as
  *
- * sg_set_page(virt_to_page(some_ptr));
- * sg->offset = (unsigned long) some_ptr & ~PAGE_MASK;
+ * sg_set_buf(sg, some_ptr, length);
  *
  * and that's it. There's no excuse for not highmem enabling YOUR driver. /jens
  */